Many types of implantable leads are currently used to treat a variety of maladies. In one example, a multiple electrode contact lead is used to treat chronic pain through stimulation of the spinal cord. “Electrode contact” will be used herein to refer to that conductive surface on the lead that delivers or sinks electrical current to or from tissue. Typical electrode contact material are platinum or platinum/iridium alloy.
Spinal cord stimulation systems generally have two implantable components: an implantable pulse generator (IPG) and at least one stimulation lead connected to one output of the IPG. Generally, however, the IPG is a multi-channel device capable of delivering electrical current through the multiple electrode contacts of the lead.
The term “lead” used herein will refer generally to any elongate device having any conductor or conductors, covered with an insulated sheath and having at least one terminal (connector) contact attached to the elongate device, usually at the proximal portion of the elongate device. As broadly used, the term “lead” may refer to a “stimulation lead” such as a percutaneous or linear lead, a paddle type lead, an extension lead or an adapter lead, which is a type of extension lead. A stimulation lead may have a stylet lumen running through most of the length of the lead and which lumen has an opening at the proximal end of the lead. A stylet, which is a thin wire or wire-like implement made from metal or some other stiff and resilient material, e.g., ceramic or plastic, may be placed into the stylet lumen during steering and implantation of the lead. The stylet, inserted into the lumen, can help stiffen the lead so that the stylet/lead combination may be more easily inserted through tissue. After the lead is positioned at a desired location in the body, the stylet is withdrawn from the stylet lumen and then the stylet is typically discarded.
There are two types of stimulation leads that may be used with the IPG. The first type of stimulation lead is a paddle lead, which has a multiplicity of electrode contacts spread out over a flat, paddle-like surface that is attached to one end of the lead. A paddle lead advantageously permits the electrode contacts to be spaced apart to provide wide coverage over a stimulation area. A disadvantage presented with a paddle lead is that it usually requires a laminectomy or laminotomy, which are highly invasive surgical procedures necessary to implant the large, non-isodiametric paddle.
A second type of stimulation lead is commonly used is a “percutaneous” or “linear” lead, having multiple electrode contacts positioned along the distal portion of the lead. U.S. Pat. No. 6,205,361 issued to Baudino et al., for example, describes the making of a multi-contact electrode array for a lead. The distal end of the lead may be about the same thickness or diameter as the remainder of the lead. Such a lead is sometimes also referred to as an “isodiametric” lead because the lead may have the same thickness or, in the case of a lead have a circular cross-section, the same diameter, along the length of the lead. The percutaneous (linear) lead is dimensionally configured for tunneling to a target stimulation site. No invasive surgical procedure such as a laminotomy is required; the percutaneous lead may be placed through an epidural type large-bore needle reducing surgical trauma.
Whether the lead is a stimulation lead such as a paddle type or a percutaneous lead or whether the lead is an extension lead or an adapter type lead, it is sometimes desired to control the stiffness and flexibility of the proximal (terminal or connector) portion of the lead relative to the remainder of the lead.
It would be desirable to have designs and methods for making the proximal (terminal) connector portion of a lead having multiple terminal contacts, which designs and methods yield a connector portion with a desired stiffness, flexibility and buckling resistance.